1. Field of the Invention
The present invention relates to methods for increasing the level of 2-methyl-2- butene in isoamylene, and particularly for converting 2-methyl-1-butene isoamylene into 2-methyl-2-butene isoamylene.
2. Discussion of Background and Material Information
Isoamylene is a component of a C.sub.5 refinery stream. The C.sub.5 portion of such hydrocarbon streams typically contain at least two isoamylene monomers, i.e., 2-methyl-1-butene and 2-methyl-2-butene in a weight ratio of about 1:1 to about 1:4, and most often about 1:2, respectively.
The separation of isoamylene from other C.sub.5 components by fractionation is somewhat difficult because of the closeness of their boiling points, i.e., less than about 10.degree. F. for many of these components. In order to recover the isoamylene content of such a mixture by conventional fractionation, a plurality of steps, for example as disclosed in U.S. Pat. No. 3,236,908, are typically reqired. Each of the fractionations resulting from the multi-step process, however, must be subjected to a further separation of components boiling within a relatively narrow range which requires the employment of complex and expensive equipment.
U.S. Pat. No. 3,236,908, SANFORD et al., attempt to obviate the need for such complex and expensive fractionation equipment by providing a method for producing isoamylene, which is predominantly 2-methyl-2-butene, from the 2-methyl-1-butene present in catalytic gasoline in which a liquid-phase, ambient-temperature, selected isomerization step is used. In their process, the effluent from a catalytic cracking of gas oil is fractionated to produce an overhead fraction consisting essentially of 2-methyl-1-butene and lower boiling C.sub.5 hydrocarbons substantially free of higher boiling materials. The fraction thus obtained is then admixed with sulfuric acid of from 60 to 70% by weight concentration with respect to water in order to isomerize 2-methyl-1-butene to 2-methyl-2-butene. The sulfuric acid phase is separated from the hydrocarbon phase and the hydrocarbon phase is then fractionated to recover 2-methyl-2-butene as product.
U.S. Pat. No. 4,447,668, SMITH, Jr. et al., are directed to a method for producing high purity tertiary C.sub.4 and C.sub.5 olefins by the disassociation of corresponding alkyl ethers and the subsequent dimerization of the olefins to produce high purity dimers thereof. In one embodiment of their process, a feed stream of C.sub.1 through C.sub.6 alkyl tertiary amyl ether is vaporized and a feed stream in a vaporized state is passed through a fixed bed cationic acidic exchange resin whereby the ether is at least partially disassociated and the disassociation product stream from the catalyst bed contains isoamylene, alcohol corresponding to the alkyl radical and unreacted alcohol tertiary amyl ether. The alcohol is then removed from the disassociation product stream prior to fractionating the condensed stream, which is predominantly isoamylene and unreacted ether feed, to recover isoamylene.
In addition to the foregoing, a number of other methods have been proposed for producing tertiary olefins from alkyl tert-alkyl ethers using various catalysts.
For example, U.S. Pat. No. 4,398,051 uses aluminum compounds supported on silica or other carriers. U.S. Pat. No. 4,320,232 employs phosphoric acid on various supports. British Patent No. 1,173,128 uses metal-containing weakly acidic components on a carrier of 20M.sup.2 /gm surface area. U.S. Pat. No. 4,398,051 attempts to produce tertiary olefins from alkyl tert-alkyl ethers utilizing carriers alone in the decomposition of methyl tertiary butyl ether. To this end, U.S. Pat. No. 4,254,290 utilizes H.sub.2 SO.sub.4 -treated clay in the decomposition of t-alkyl ether-alkynols.
U.S. Pat. No. 4,691,073, MICHAELSON discovered that high purity olefins are obtainable in extremely high yields over a sustained period by bringing alkyl tert-alkyl ethers into contact with a specified catalyst, i.e, clays treated with hydrofluoric acid and/or hydrochloric acid.
S.U. 644,767, CHAPLITS, is directed to obtaining increased yields of 2-methyl-2-butene by isomerization of 2-methyl-1-butene in the presence of a catalyst composed of a moulded sulpho-cation exchange resin with a thermoplatic material, such as polypropylene and polyethylene, in the presence of methyl-tert-amyl ether tert-amyl alcohol, ethyl alcohol acetone or mixtures thereof, used as 5-10% by wt. of the initial material at a temperature between 60.degree.-80.degree. C., and preferably 70.degree.-80.degree. C., and a pressure of 2.5-4.5 atmospheres.
It is known that tertiary olefins may be prepared by reacting them selectively from petroleum feeds with a primary alcohol in the presence of an acid catalyst to produce the corresponding alkyl tert alkyl ethers. Such alkyl tert-alkyl ethers may then be separated and subsequently decomposed back to the tertiary olefins and the primary alcohol.
For example, European Patent Application No. 123,338, GROENEVELD, is directed to the process for preparation of methyl tertiary butyl ether (MTBE) by reacting isobutene with methanol in the presence of an acid catalyst to yield MTBE followed by conversion of normal butenes present in the hydrocarbon flow to isobutene followed by passing the mixture thus obtained to a reaction zone to form MTBE.